Plasmonic-resonant bowtie antenna for carbon nanotube photodetectors

The design of bowtie antennas for carbon nanotube (CNT) photodetectors has been investigated. CNT photodetectors have shown outstanding performance by using CNT as sensing element. However, detection wavelength is much larger than the diameter of the CNT, resulting in small fill factor. Bowtie antenna can confine light into a subwavelength volume based on plasmonic resonance, thus integrating a bowtie antenna to CNT photodetectors can highly improve photoresponse of the detectors. The electric field enhancement of bowtie antennas was calculated using the device geometry by considering fabrication difficulties and photodetector structure. It is shown that the electric field intensity enhancement increased exponentially with distance reduction between the CNT photodetector to the antenna. A redshift of the peak resonance wavelength is predicted due to the increase of tip angles of the bowtie antennas. Experimental results showed that photocurrent enhancement agreed well with theoretical calculations. Bowtie antennas may find wide applications in nanoscale photonic sensors. Copyright © 2012 Hongzhi Chen et al.Link_to_subscribed_fulltex

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Development and testing of nano robot end effector for cell electrophysiology and elastography studies

Electrophysiology and elastrography provide significant information in biological and biomedical studies. Conventional atomic force microscopes (AFMs) have been used for the mechanical characterization of living cells, but they lack the capability to measure the electrical properties of biological cells and tissues. In this work, a novel nano robot end effector has been developed to perform multidimensional measurement of cells. The end effector is designed for characterization of soft materials and it includes an embedded metal electrode for membrane potential measurement of cells. © 2011 IEEE.Link_to_subscribed_fulltex

Nanomaterials Processing for Device Manufacturing

Carbon nanotubes (CNTs) are known to be a very unique material for various kinds of practical nanodevices. Due to large variations in electronic properties of CNTs and their extremely small size, a systemic approach for large-scale production of CNT-based nanodevices with consistent properties is still lacking. Manipulation and classification of CNTs is challenging and is not easily implemented by using the traditional robotic system. This chapter presents a new approach to classify and deposit nanotubes that provides an effective and reliable means to manufacture CNT-based devices. Homogeneous nanotubes can be precisely selected by using a microfluidic system and applying electrokinetic force to grade the nanotubes based on their electronic properties. Results indicated that directions of dielectrophoretic forces on different types of CNTs could be controlled by varying the frequency of the applied electric field. Repeatable and consistent experimental results of multiple CNT-based devices have been obtained by using the separation and deposition processes. Hence, the system provides a batch manipulation of CNTs for device manufacturing. As a result, this enhances the manufacturing and assembly of CNT-based nanodevices, which is important for the development of future nano-optoelectronic sensors and devices. © 2012 Elsevier Inc. All rights reserved.Link_to_subscribed_fulltex

Carbon nanotube-based non-cryogenic cooled spectrum IR detectors

Carbon nanotube (CNT) has been found to be one of the promising materials for efficient detection and used in different nanoelectronic devices due to its unique electrical properties. Recently, the applications of nanostructural material to infrared (IR) sensors are considered. Our group has developed non cryogenic cool and multiple spectrums optical sensors using single CNT and demonstrated the good sensitivity of CNT to the infrared light in different ranges. In this paper, design, fabrication and experimental result of the CNT-based optical sensor were described. The results indicated the band gap of CNTs can be tuned by electrical breakdown process, resulting multiple spectrum sensors can be developed by controlling the band gap of CNTs. Moreover, the CNT-based optical sensor detected the near-IR (NIR) signal and middle-wave IR (MWIR) signal in room temperature environment, the temperature dependency of the sensors has been studied. © 2009 SPIE.Link_to_subscribed_fulltex

Comparative studies of Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance with Dissipation (QCM-D) for real-time identification of signaling pathway

Cell signaling is one of the fundamental processes that control the cell fate. It modulates the cell shape and mechanics. To identify the dynamic signaling pathway in situ, we need tools that are capable of monitor the real-time elasticity and viscosity changes as well as structural rearrangements. Atomic Force Microscopy (AFM) has been demonstrated to be an effective instrument to visualize membrane and cytoskeleton structures on live cells. It can also provide the mechanical stiffness information by recording force displacement curves. Meanwhile, the viscoelasticity change by signaling pathways can be measured as the change of dissipation of a monolayer of cells by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). In the current study, we use the human epidermoid carcinoma A431 cell line as a model system which will be stimulated by epidermal growth factor (EGF). AFM was first used to image the structure of live A431 cells before and after stimulation; force measurement was also performed to analyze the dynamic elasticity change. The change of viscoelasticity of the A431 cell induced by EGF was monitored in real time on a QCM-D in terms of dissipation change and frequency shift. The mechanical property measurements from AFM and QCM-D experiment was analyzed and compared. Quantitative analysis can be performed to obtain the dynamic modulus of the material through theoretical modeling. This novel combination can be complementary to each other. A unified profile can therefore be generated as an effective indicator of signaling pathways such as cell proliferation and apoptosis. ©2010 IEEE.Link_to_subscribed_fulltex

Nanoantennas on Nanowire-Based Optical Sensors

This chapter presents a theoretical analysis and experimental study with regard to nanoantennas for use with carbon nanotubes (CNT) -based IR sensors. It presents a comprehensive mathematical model that accounts for the quantum-confinement effects on the conductivity and dielectric function of the nanoscale antenna-to theoretically predict the electric field-enhancement effect for different configurations of the antenna structure and the CNT sensor. In addition, it describes the design and fabrication process for nanoantennas for quantum IR detectors. By integrating the nanoantenna, the incident electric field at the sensor was enhanced such that the photocurrent of the sensor was greatly increased. Several factors for affecting the gain of the antenna are discussed and their effects are demonstrated and compared to the response of the detector with antennas of different geometries. Based on this understanding, the developed enhancement technology provides a dramatic improvement in the performance of infrared sensors. In the future, it is anticipated gaining greater insight into the localization of light and its control relating to semiconductor nanostructures. To date, localization of light has only been achieved using metallic nanostructures. © 2012 Elsevier Inc. All rights reserved.Link_to_subscribed_fulltex

Nanoresonant signal boosters for carbon nanotube based infrared detectors

We report the development of a sensitive carbon nanotube (CNT) infrared detector whose signals are boosted by nanoantenna-like features. This assembly is fabricated using nanoassembly of CNTs and a standard photolithographic process, together with nanoantenna-like features that are designed to create a resonance structure necessary to boost the electric field intensity at the CNT sensor. A novel approach is employed to find the near-field effect of the antenna. As a result, these effects are verified and demonstrated experimentally in this paper. The first experimental demonstration of a practical infrared device with nanoantenna-like structures is reported; it shows that the photocurrent is increased by an order of magnitude. The proposed fabrication and design process enables a ready integration of resonance structures into the manufacture of infrared devices, and opens the possibility of developing high fidelity infrared sensors with wide sensing range. © 2009 IOP Publishing Ltd.Link_to_subscribed_fulltex

Carbon nanotube-based noncryogenic cooled multispectrum focal plane array

This paper presents the development of non-cryogenic-cooling spectrum infrared (IR) focal plane array (FPA) using a single carbon nanotube (CNT). The FPA consists of an array of CNT-based photodiodes. The CNT-based photodiodes can be made by our nanomanufacturing process and band gaps of CNTs can be tuned precisely by the electric breakdown system. As a result, the CNT-based photodiodes with high sensitivity at a special wavelength can be achieved. In this paper, design, fabrication and experimental results of the CNT-based IR photodiode are reported. The results indicate that CNTs are very sensitive of middle-wave IR (MWIR) signal at room temperature. Moreover, the performances of the photodiodes have been evaluated. These results suggest that CNTs can be used in high throughput sensing applications. © 2010 Copyright SPIE - The International Society for Optical Engineering.Link_to_subscribed_fulltex

High-speed non-cryogenic cooled infrared sensors using carbon nanotubes

We report the development of high-speed carbon nanotube (CNT) based infrared (IR) sensors which operate at room temperature. When a single CNT is manipulated between two different metal electrodes, a Schottky diode is formed at the CNT-metal interface, so photocurrent is generated when there is IR illumination. The devices exhibit a fast optical response time of 15 μs and the response time is limited by the readout circuit during the measurement. Beside, we proved CNTs are less temperature-dependent. Dark current of CNTs changes by a factor of 10 for 200 °C drop in temperature, and photocurrent is also maintained in the same level. These values indicated nanotube can be used as an excellent IR sensing material with high-speed, stable and reliable performance under non-cryogenic cooled environment. ©2010 IEEE.Link_to_subscribed_fulltex